The present invention relates to apparatus for improved aftertreatment of textile material by application of microwaves, and more particularly relates to a novel apparatus used for improvement in effective drying of scoured or dyed textile material by means of irradiation of microwaves.
Fixing and development of dyes on dyed textile material have long been carried out by means of steaming the dyed textile material after interposed drying.
As a substitute for the steaming process, it has recently been proposed to apply microwaves to dyed textile material in wet state. Here, the word "microwaves" refers to electromagnetic waves whose frequencies are in a range from 300 to 30,000 MHz.
Microwaves have a number of notable merits in particular when they are used in treatment of textile material in wet state. Firstly, they permeate into the textile material extremely quickly and heat it within a very short time. Secondly, since generation of heat by microwave application is caused by dielectric loss, the microwaves are selectively absorbed in objects with large dielectric loss and heat the necessary or desired object only whilst avoiding heating of the unnecessary or undesired object or objects. Thirdly, the treated textile material generates heat by itself when subjected to microwave irradiation and the heat so generated warms the ambient atmosphere. Consequently, there is no need at all for any additional heating equipment which should otherwise be used for raising the temperature of the ambient atmosphere. This automatic generation of heat by the textile material assures a high rate of thermal efficiency in the process. Fourthly, since the microwaves cause a simultaneous temperature rise at different sections of the treated material, difference in temperature between the core and surface sections of the material is very small, thereby assuring ideally uniform heating of the material. Fifthly, the heating condition in the process can simply and freely be controlled in accordance with requirements in the actual treatment by adjustment of the output voltage used for microwave generation.
Irradiation of microwaves onto a textile material causes ionic conduction and dipole rotation of the fibers composing the textile material and water and/or agents contained in the materials and such ionic conduction and dipole rotation will cause rapid and uniform heating of the textile material.
A wide variety of systems have been proposed in order to practice the above-described microwave irradiation in treatment of textile materials, but quite a few of them have not been feasible on a practical industrial scale.
One cause for this difficulty resides in the manner of irradiation of microwaves. An applicator is generally used for this purpose and the conventional applicators are roughly classified into these types, i.e. an applicator with a hairpin curved waveguide, an applicator with a densely hairpin curved waveguide, and an oven-type applicator.
In the case of the applicator using the waveguide, heating effect is greatly affected by wave length of the microwave irradiated and this delicate influence tends to cause uneven heating of the material subjected to the treatment. Consequently, the applicators of these types are unsuited for treatment of dyed or scoured textile materials, which required a high rate of uniformity in the heating effect.
In the case of the oven-type applicator including a metallic hexahedral irradiation chamber, it is necessary to employ any expedient to equalize the strength of the magnetic field surrounding the material in the chamber. Otherwise, the applicator of this type is quite unsuited for use on practical industrial scale although it may operate in order in laboratories.
The other cause for the above-described difficulty resides in fusion of fibers composing a textile material during, or as a result of, heating by application of microwaves. This is in particular a serious problem when the textile material is composed of thermoplastic synthetic fibers such as acrylic fibers. Such fusion of the textile material is caused by a temperature rise of the water used as a dyeing medium and/or of a high boiling point agent or agents as assistants, both being contained in the textile material after dyeing. For example, in the case of a textile material made of acrylic fibers which can be dyed at a temperature close to the boiling point of pure water, swelling of the dyed fibers starts at a temperature close to 100.degree. C. and, regardless of its dielectric constant, dipole rotation occurs in the fibers, which causes abrupt evacuation of water, temperature rise and eventual fusion of the fibers. In order to prevent such fusion of fibers composing the textile material, it is absolutely necessary to prevent evacuation of water contained in the fibers during the treatment.
A further cause for the above-described difficulty resides in the manner to prevent the above-described evacuation of water contained in the fibers during the treatment. For this effect, a textile material is transported through a microwave applicator zone or zones while being clamped between a pair of running endless belts or being placed in surface contact with a wet sheet. In either case, possible contamination on the belts or sheet tends to develop blemishes on the textile material, which greatly degrades its commercial value.